SPs are cheap and do work well, but not always! Also I get bored pretty quickly with them, particularly if working them slowly or dead drifting with the current - often successful methods. Nothing compares to the visual excitement of the topwater 'walk -the-dog' stuff for me (hence the moniker). I haven't yet found the need to spend over £15 on a lure but I have borrowed some of the very expensive ones just to see how they work and to make direct comparisons to similar but cheaper models as well as copies/clones. Not all of the cheaper lures work as they should and you can easily end up wasting a lot of money finding good ones. Even then they often need tuning to run properly - see the Rapala info on tuning lures if you haven't already, and experiment! It really can make a massive difference as can weighting/changing hooks or adding ballast like lead foil to the body of the lure.
There are a few lures in the up to £15 bracket like the Duo Realis Pencil and YoZuri Jointed Crystal Minnow that I go out of my way to buy because they have repeatedly proved to work so damned well straight out of the box. Equally there are cheaper metal lures like the Seeker that have also earned a place in my armoury as a long casting fish catcher. It's certainly not all about hard plastics, more about having the correct tools for specific jobs for me. SPs are part of that. All good lures are certainly cost effective, and whilst I dare say I could do pretty well just using lures from the Savage Gear range (good value brand in my opinion, certainly the ones I own), it's nice to have a few too many and buy a few treats occasionally! I don't loose many lures as I'm not shore fishing really snaggy ground that often, but even from the boat the occasional loss just has to be accepted.